Uterine leiomyomas, commonly called fibroids, are a major health concern for women of reproductive age. The objectives of the study described herein are to investigate the growth dynamics of uterine leiomyomas in a clinically relevant population of women. Basic questionsof interest in this project are test the hypotheses that uterine leiomyomas are heterogeneous in terms of their growth characteristics and in their clinical symptoms or outcomes, and that differences in leiomyoma growth dynamics can be discriminated by molecular markers and cellular phenotypes. Study included about 115 premenopausal women (>18 years old) with at least one uterine leiomyoma. The inclusion criteria for patient enrollment is confirmed diagnosis of leiomyoma by ultrasound. At least one leiomyoma must be equal to or greater than 2 cm in diameter or the uterus must be enlarged to the size typical during the eighth week of pregnancy (indicating many leiomyomas are present). After enrollment and informed consent, T1- and T2-weighted magnetic resonance image (MRI) scans were conducted beginning at the first visit and then at 3, 6, and 12 months. Each patient had a physical exam and provided urine and blood samples at each MRI visit, and responded to an initial extensive telephone-administered questionnaire followed by abbreviated monthly questionnaire updates. Of these, 28 women required surgical intervention (hysterectomy/ myomectomy). Leiomyoma samples from these women were analyzed for histopathological and molecular changes correlated with growth. The specific aims of the study are to: (1) investigate leiomyoma growth as a function of multiplicity and location; (2) examine the relationship between leiomyoma growth and clinical symptoms or outcome; (3) identify molecular, cellular, and pathological characteristics of leiomyomas with differing growth dynamics; and (4) examine endocrinological parameters and lifestyle factors related to differential growth dynamics of uterine leiomyomas.